Masahiro Nada

Triple-mesa Avalanche Photodiode With Inverted P-Down Structure for Reliability and Stability

A 25-Gbit/s avalanche photodiode (APD) using an inverted p-down structure and triple-mesa structure for eliminating an edge breakdown and reducing an electric field at a surface of the device is proposed and examined. Active area dependence of dark current and activation energy as small as 0.17 eV strongly suggest that the surface leakage current is negligible, and the edge breakdown does not occur. As for RF characteristics, sufficient 3-dB bandwidth of 18 GHz for 25-Gbit/s operation is obtained. We experimentally find that our triple-mesa inverted structure successfully eliminates the possible components which affect the reliability and stability of the APDs.

25-Gbit/s burst-mode optical receiver using high-speed avalanche photodiode for 100-Gbit/s optical packet switching

25-Gbit/s error-free operation of an optical receiver is successfully demonstrated against burst-mode optical input signals without preambles. The receiver, with a high-sensitivity avalanche photodiode and burst-mode transimpedance amplifier, exhibits sufficient receiver sensitivity and an extremely quick response suitable for burst-mode operation in 100-Gbit/s optical packet switching.

Inverted InAlAs/InGaAs Avalanche Photodiode with Low?High?Low Electric Field Profile

We propose a new p-down inverted avalanche photodiode (APD) structure suitable for a scaled APD with smaller junctions. The inverted APD structure has an edge-field buffer layer to prevent undesirable edge breakdown and suppress the excess surface leakage current associated with the InGaAs mesa surface. The fabricated back-illuminated InAlAs/InGaAs APDs show excellent multiplication characteristics without edge breakdown. An f3dB of 27 GHz and a GB product of 220 GHz are obtained for these APDs.

50-Gbit/s vertical illumination avalanche photodiode for 400-Gbit/s Ethernet systems

50-Gbit/s error-free operation is demonstrated by a high-speed avalanche photodiode for the first time. The APD exhibits 3-dB bandwidth of 35 GHz and excellent receiver sensitivity of -10.8 dBm at a BER of 10(-12) against non-return to zero input optical signals. These results indicate our APD is promising for the systems with serial baud rate of 50 Gbit/s such as 400-Gbit/s Ethernet systems.

Design and Performance of High-Speed Avalanche Photodiodes for 100-Gb/s Systems and Beyond

This paper reviews our work on high-speed avalanche photodiodes (APDs) with a unique vertical-illumination structure, targeting 100-Gb/s systems and beyond. The APDs feature easy lateral and vertical scaling for achieving the required operation speed and responsivity. For 100-Gb/s systems, a 3-dB bandwidth of 18.5 GHz with multiplied responsivity of 9.1 A/W is obtained. For larger capacity applications such as 400-Gb/s systems, a maximum 3-dB bandwidth of over 35 GHz and responsivity at a gain of unity of almost 0.7 A/W are obtained by reducing diameter of an n-contact mesa and optimizing thickness and configuration of an absorption layer.

High-Speed Avalanche Photodiode and High-Sensitivity Receiver Optical Subassembly for 100-Gb/s Ethernet

This paper reviews a 25-Gb/s avalanche photodiode (APD) with an inverted p-down structure and its application to a 100-GbE receiver optical subassembly (ROSA). The APD exhibits high responsivity (0.9 A/W), large bandwidth (18 GHz at

Electric Characteristics of Li2O-Doped TiO2 Nanocrystalline Film and Its Application to Dye-Sensitized Solar Cells

M = 10

High-speed avalanche photodiodes for 100-Gb/s systems and beyond

), and a large gain-bandwidth product (235 GHz) by optimum design of the absorption layer (1.0 μm) and InAlAs avalanche layer (0.1 μm). Stable I-V characteristics without edge breakdown were observed owing to a strong confinement of a high electric field in the avalanche layer by two field-control layers and a triple-mesa structure. We also describe a 100-Gb/s (4 × 25-Gb/s) ROSA using a monolithic four-channel APD array and an ultrasmall planar-lightwave-circuit demultiplexer. The performance indicates a record minimum receiver sensitivity of -20 dBm and 50-km error-free transmission without an optical amplifier.

Vertical illumination InAlAs avalanche photodiode for 50-Gbit/s applications

The effects of Li2O doping on TiO2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO2 nanocrystalline film. The temperature dependence of carrier concentration and electric conductivity of Li2O-doped TiO2 nanocrystalline film are determined by Hall effect and high-impedance conductivity measurements. At the doping condition of 4.5 ×10-5 molar ratio of Li2O to TiO2, the electric conductivity at room temperature is maximum, which is almost two orders of magnitude higher than that of the undoped sample. The conduction type and carrier concentration at 500 K are n-type and 1.75 ×1013 cm-3, respectively. From the temperature dependence of the electron concentration, the donor depth is estimated as 1.0 eV. By applying Li2O doping to DSC, the conversion efficiency and open-circuit voltage are maximum at the highest conductivity of the Li2O-doped TiO2 layer.

A High-Linearity Avalanche Photodiodes With a Dual-Carrier Injection Structure

This talk reviews our work with avalanche photodiodes (APDs) with unique vertical-illumination structure. The APD features 3-dB bandwidth of 18.5 GHz with multiplied responsivity of 9.1 A/W, satisfying requirements for 100-Gb/s systems. Further high-speed characteristics targeting 50-Gb/s are also discussed.